1. Field of the Invention
The present invention relates to a keyless entry system apparatus which performs locking and unlocking operations of a door of a vehicle by means of radio communication between a vehicle device and a portable device, more particularly, to a keyless entry system apparatus which can accurately determine whether the portable device is positioned inside or outside of a predetermined interface.
2. Description of the Related Art
Conventionally, there has been provided a keyless entry system apparatus which performs locking and unlocking operations of a door of a vehicle by means of radio communication between a vehicle device and a portable device. In addition, there has been recently provided a passive keyless entry system apparatus which performs locking and unlocking operations of a door of a vehicle, as ID codes preset in each portable device are verified by performing communication between the vehicle device and the portable device when the portable device approaches the vehicle. This kind of keyless entry system is disclosed in, for example, JP-A-2002-77972.
In particular, in the passive keyless entry system apparatus, it is important to determine whether the portable device is positioned inside or outside of the vehicle. For this reason, in the vehicle device, a plurality of transmitting antennas is provided in each place of the vehicle. When the portable device receives radio wave from the transmitting antenna inside the vehicle, it is determined that the portable device is inside the vehicle. When the portable device receives radio wave from the transmitting antenna outside the vehicle, it is determined that the portable device is outside the vehicle.
However, in the keyless entry system apparatus according to the related art, the determination of the position of the portable device is not sufficiently accurate. For example, as a radio wave leaks from the transmitting antenna inside the vehicle, the portable device may incorrectly determine that the portable device is inside the vehicle when the portable device is in fact outside the vehicle. On the contrary, as a radio wave leaks from the transmitting antenna outside the vehicle, the portable device may incorrectly determine that the portable device is outside the vehicle when the portable device is in fact inside the vehicle. When a transmission power of radio wave from the transmitting antenna is weakened to prevent the leakage of the radio wave, the portable device occasionally cannot receive radio wave even though the portable device is inside the vehicle, which may cause incorrect determination.
In JP-A-2002-77972, each of the transmitting antennas of the vehicle detects reception intensity, and an area is determined where the portable device exists, with respect to the reception intensity. However, incorrect determination may occur in this case as well, and thus the determining accuracy of the position of the portable device is not sufficient.
In addition, the determination of the position of the portable device is not limited to the inside and outside of the vehicle, the position of the portable device may be determined whether it is inside or outside of a place separated from a door at a predetermined distance. In this case, for example, it is possible to turn on a lamp when the portable device gets close to the door within the predetermined distance. For this reason, a keyless entry system is required whose determination of the position is not limited to the inside and outside of the vehicle, but may include the inside and outside of a predetermined interface.